1. Field of the Invention
The present invention relates to a drive apparatus for moving an object (driven object) in a desired direction.
2. Description of the Prior Art
An example of the prior art having this type of drive apparatus is the positioning table shown in FIG. 1.
As shown in FIG. 1, two rotors in the form of toothed belt pulleys 1 and 2 are arranged separated from each other on a base (not shown) equipped on the positioning table. A belt-shaped member in the form of endless toothed belt 3 is wrapped around these toothed belt pulleys 1 and 2. In addition, a driving device in the form of motor 5 is provided that drives toothed belt pulley 1 by applying torque.
Another toothed belt pulley 6 is arranged in close proximity to the above-mentioned toothed belt pulley 1, and the toothed belt pulley 6 engages with toothed belt 3. In addition to this toothed belt pulley 6 acting as a device for maintaining opposing portions 3a and 3b of opposing toothed belt 3 parallel with each other between the above-mentioned toothed belt pulleys 1 and 2, it also applies the required tension to toothed belt 3.
Driven object 7 to be moved is provided between toothed belt pulleys 1 and 2. Said driven object 7 is composed of moving table 8 and sliding unit 9 coupled to the bottom surface of said moving table 8. Sliding unit 9 is straddled over track rail 10 and guided by track rail 10.
At least a portion of driven object 7 , composed of the above-mentioned moving table 8 and sliding unit 9, is arranged so as to be surrounded by endless toothed belt 3, and is also coupled to toothed belt 3.
In the drive apparatus, toothed belt 3 is driven as the result of torque being applied to toothed belt pulley 1 by motor 5. Driven object 7 coupled to said toothed belt 3 then moves along track rail 10.
In the above-mentioned drive apparatus of the prior art, the center of motor 5 directly coupled to toothed belt pulley 1 in order to apply torque to said toothed belt pulley 1 is located at a position away from a line 7a extending from the center in the direction of the width of driven object 7 . Accordingly, this drive apparatus has the disadvantage of motor 5 approaching one side together with the inclined portion 3c of toothed belt 3 only existing at a single location on the other side thus preventing lateral symmetry with respect to the overall apparatus.
Furthermore, although not shown in the drawings, devices that are able to solve the above-mentioned problems have also been considered. In one device, two toothed belt pulleys having a diameter smaller than the above-mentioned toothed belt pulley 6 are provided at laterally symmetrical locations instead of said toothed belt pulley 6. These two toothed belt pulleys are engaged with each of opposing portions 3a and 3b of toothed belt 3. In another device, a toothed belt pulley having the same diameter as toothed belt pulley 2 and engaging with said opposing portions 3a and 3b at both their right and left sides is arranged on said extending line 7a instead of the above-mentioned toothed belt pulley 6, with motor 5 arranged on said extending line 7a.
However, in the former constitution, since two toothed belt pulleys of the same diameter as well as two sets of mechanisms and so forth that support these pulleys while allowing them to rotate freely, are required. Thus the number of parts increases resulting in increased costs. In addition, with respect to the latter device, since a single toothed belt pulley engages at two locations with respect to toothed belt 3, namely at the above-mentioned opposing portions 3a and 3b, toothed belt 3 becomes excessively long thus resulting in cases wherein matching the engaging states at the two locations is difficult.